Oil-shales of this type contain carbonates and silicates and generally have properties roughly as follows:
Maximum heating power--1,000 Cal/kg PA1 Organic matter--20% by weight PA1 Ash--65% by weight PA1 Water content--15% by weight PA1 providing a drying gas by mixing hot gas taken from the combustion chamber with relatively cool gas taken from the chimney, the proportions of said gasses being adjusted as a function quantity of water in said damp shale; PA1 crushing lumps of said shale in a crusher and in the presence said drying gas; PA1 injecting the resulting grains of crushed shale together with the hot gas into an expansion chamber in which the major portion of the grains falls out from the drying gas, while the lightest portion of grains is entrained by the gas; PA1 passing the drying gas together with said lightest portion of grains entrained thereby through filter means to separate said lightest portion of grains from the drying gas; PA1 riddling said major portion of the grains to provide a larger grain fraction and a smaller grain fraction; PA1 recycling said larger grain fraction through said crusher; PA1 combining said smaller grain fraction with the said lightest portion of grains separated by said filter means; and PA1 injecting the combined grains into said combustion chamber in a suspension in primary air. PA1 a combustion chamber having a chimney; PA1 means for mixing hot gas taken from the combustion chamber with relatively cool gas taken from the chimney to provide a drying gas, the proportions of said gasses being adjusted as a function quantity of water in said damp shale; PA1 a crusher for crushing lumps of said shale in the presence said drying gas; PA1 an expansion chamber for receiving grains of crushed shale together with the hot gas from said crusher, the major portion of the grains falling out from the drying gas in said expansion chamber, while the lightest portion of grains is entrained by the gas; PA1 means for conveying the drying gas together with said lightest portion of grains entrained thereby to filter means for separating said lightest portion of grains from the drying gas; PA1 riddling means for riddling said major portion of the grains to provide a larger grain fraction and a smaller grain fraction; PA1 means for recycling said larger grain fraction through said crusher; PA1 means for combining said smaller grain fraction with the said lightest portion of grains separated by said filter means; and PA1 means for injecting the combined grains into said combustion chamber in a suspension in primary air.
Oil-shales have already been burned in boilers having mechanical gratings. Such boilers are only acceptable for burning relatively low hourly tonages of fuel.
It might be thought that the techniques used for burning low quality coals or lignites could be transposed to burning such oil-shales. However, the high proportion of silica-rich, abrasive ash contained in such oil-shales would lead to the crushers consuming a large amount of energy and to excessive wear thereof.
Further, due to their low heating power, such oil-shales require large quantities of gas for drying and for transport after crushing. Air cannot used both for this purpose and for supplying the oxygen for combustion in the combustion chamber, since the resulting combustion would be incomplete and of poor quality.
Preferred implementations of the present invention remedy these difficulties by providing a method in which damp oil-shale is crushed without excessive consumption of energy nor excessive wear of the crusher, in which the smallest grains from the crusher are readily extracted for burning, and in which satisfactory combustion is obtained in the combustion chamber.